Since thrombopoietin is a polypeptide cytokine consisting of 332 amino acids and it promotes platelet production by stimulating differentiation and proliferation of a megakaryocyte via a receptor, it is expected as an agent for morbidity of a blood disease accompanied with abnormality of the platelet number such as thrombocytopenia. A nucleotide sequence of a gene encoding a thrombopoietin receptor is described in Non-Patent Document 1. In Patent Document 1 and Patent Document 2, low-molecular peptides having affinity for the thrombopoietin receptor are also known, but oral administration of these peptide derivatives are not generally practical.
As a low-molecular compound having affinity for the thrombopoietin receptor, a 1,4-benzothiazepine derivative is described in Patent Document 3 and Patent Document 4, a 1-azonaphthalene derivative is described in Patent Document 5, and a 1,3-thiazole derivative is described in Patent Document 6 to 22.
[Patent Document 1]
                Japanese Patent Application Laid-Open (JPA) No. 10-72492[Patent Document 2]        International Publication WO 96/40750[Patent Document 3]        JP-A No. 11-1477[Patent Document 4]        JP-A No. 11-152276[Patent Document 5]        International Publication WO 00/35446[Patent Document 6]        JP-A No. 10-287634[Patent Document 7]        International Publication WO 01/07423[Patent Document 8]        International Publication WO 01/53267[Patent Document 9]        International Publication WO 02/059099[Patent Document 10]        International Publication WO 02/059100[Patent Document 11]        International Publication. WO 02/059100[Patent Document 12]        International Publication WO 02/062775[Patent Document 13]        International Publication WO 2003/062233[Patent Document 14]        International Publication WO 2004/029049[Patent Document 15]        International Publication WO 2005/007651[Patent Document 16]        International Publication WO 2005/014561[Patent Document 17]        JP-A No. 2005-47905[Patent Document 18]        JP-A No. 2006-219480[Patent Document 19]        JP-A No. 2006-219481[Patent Document 20]        International Publication WO 2007/004038[Patent Document 21]        International Publication WO 2007/036709[Patent Document 22]        International Publication WO 2007/054783[Non-Patent Document 1]        Proc. Natl. Acad. Sci. USA, 1992, vol. 89, p. 5640-5644        